There are many instances when the tracking of people, animals or objects is useful. Farmers may use tracking systems to track the feed and production of particular animals. These systems may also control the feeding of each animal to optimize production per unit feed or to control entry into particular areas. There are times when objects, such as parts in a flexible automated assembly plant need to be tracked and routed. Each of these tracking and control systems run into similar problems.
One of the problems that must be solved with these systems is that of transmitter collision. In any system tracking two or more objects there must be some manner of distinguishing between the particular units.
It is known in the art to provide the individual units with differing frequencies. A base unit determines which particular unit received by the wavelength of the transmission. Such a system can only be used with a relatively small number of such units because of the spectrum used. This technique tends to use a large bandwidth and requires a wide band receiver.
It is also known to employ a single wavelength with some encoded identification information as a part of the transmission. The base unit would then determine the particular unit received by the identification code. There is a problem with this technique. It is likely that two or more such units in the same vicinity will transmit at the same time. This prevents the receiving unit from distinguishing the respective identification codes.
It is known in the art to employ responsive units which transmit only in response to receipt of a signal from a base unit. Such systems include passive systems that take power from the received signal and transmit on a differing wavelength and active systems that are self powered. This technique does not prevent transmission collision. It is possible for two units to be near the base unit and respond simultaneously to the triggering signal.
Another lack in known tracking and control systems is in detection of interaction between things tracked. The prior art tracking and control systems have a remote unit mounted on the things tracked and a base unit disposed in a portal or area where control or tracking is desired. In tracking the movements of wild animals, for example, it may be desirable to determine the interaction between animals outside the range of any base unit. There is no provision for determining interactions between things to be tracked outside the range of a base unit in the prior art. This is because the portable units have no manner of detecting other portable units.
It would therefore be useful to provide a communication and identification system that prevents repeated transmitter collisions and that permits logging of interaction between units outside the range of any base unit.